Improving repair performance for damaged C/C composites via heat-treatment temperature optimization and surface pretreatment

A Ni-based solder BNi-5 was adopted as the repair agent to repair the prefabricated defects on the car-bon/carbon(C/C)composites.The effects of different heat-treatment(HT)temperatures and pre-oxidation on the chemical composition,microstructure,and mechanical behavior of the repaired C/C composites were investigated,and the repair mechanism was studied by finite element analysis methods.The repair agent and C/C composites were tightly bonded through mechanical interlocking and chemical reactions,and the flexural properties of the damaged C/C composites were significantly improved after repair.The products at the interface formed a gradient distribution structure of the thermal expansion coefficient when the HT temperature was 1300°C,which is beneficial to relieve the residual thermal stress at the interface.Meanwhile,the porosity of the surface of the C/C composites was higher after pre-oxidation,which led to more diffusion channels for the repair agent and enhanced the interface bonding ability.The flexural strength was the highest with a recovery rate of 85.2%when the C/C composites were pre-oxidized at 600°C and the HT temperature was 1300°C.This work provides a strategy for the engineering application of the damage repair of C/C composites.